Typically, a guidance or a navigation system will contain a gyroscope for determining the rate of angular motion of a vehicle. Early gyroscopes were comprised of a rotating wheel which was mounted so that its axis could turn freely in certain or all directions. These early gyroscopes were capable of maintaining the same direction in space despite the movements of its mountings and surrounding parts. Its motion was based upon the principle that a body rotating rapidly about an axis will tend to resist a disturbing change or torque by rotating slowly in a direction perpendicular to the disturbance. These early gyroscopes were mostly used in conjunction with non-precise vehicle steering equipment. Thus, these early gyroscopes were generally sufficient for determining and maintaining a relatively reliable directional heading.
However, due to inaccuracies produced by friction between moving parts, temperature changes, and inadequate manufacturing tolerances, these early mechanical gyroscopes have been replaced by other types of gyroscope devices which require no moving parts. A description of one of these other types of gyroscope devices, based on the principle of superconductivity, is disclosed in U.S. Pat. No. 3,657,927, awarded to Tyson. In this type of gyroscope, a current enters a superconducting ring where it is split into two branches. In one branch the current is traveling clockwise, and in the other branch the current is traveling counterclockwise. Both of these oppositely traveling currents pass through a Josephson junction within its respective branch. When the superconducting ring is rotated, a circulating current is generated. This circulating current causes a positive phase shift to occur in the wavefunction in one branch and a negative phase shift to occur in the wavefunction in the other branch. Upon recombination, interference is created between the two wavefunctions. This interference manifests itself as an alternating current at the output of the device. The phase change of the output current is proportional to the rotational frequency of the ring. This device is also sensitive to changes in the magnetic flux surrounding the device. These changes in the magnetic flux, due to external magnetic fields, are falsely detected as a rotation of the superconducting ring. The effect of these external magnetic fields is minimized by using a superconducting shield.
While the above-described device provides a gyroscope that is functionally non-mechanical, a problem exists with regard to the superconducting shield that this device has incorporated therein. The major problem with the superconducting shield is the formation of an internal magnetic field that develops when the superconducting shield is rotated. This magnetic field is known as the London moment field. The magnitude of this magnetic field has the same linear relationship with rotation as the above mentioned device. As the device is rotated, so is the superconducting shield. Thus, the London moment field generated by the superconducting shield has the same value as the field generated by the device. Since the shield provides a field value that minimizes the energy state of the device, the device does not react to the rotation. Therefore there is no output from the superconducting gyroscope when it is surrounded by a superconducting shield.
Accordingly, it would be desirable to overcome the problem that exists with the superconducting shield as described above, while providing a gyroscope, based on the principle of superconductivity, that is functionally non-mechanical and that is shielded from external magnetic fields.